Method and Machine for Finishing a Spherically Curved Surface Portion of a Workpiece by Means of a Finishing Tool and a Dressing Tool for the Finishing Tool

ABSTRACT

A method for finishing a spherically curved surface portion of a workpiece with a finishing tool having a machining surface includes the steps of finishing the surface portion of the workpiece, whereby the finishing tool, with at least one part of the machining surface, is brought into contact with at least one part of the surface portion of the workpiece. The workpiece and the finishing tool are rotatably driven; and dressing the finishing tool with a dressing tool having a curved dressing surface, whereby the dressing tool, with at least one part of the dressing surface, is brought into contact with at least one part of the finishing surface of the finishing tool. The finishing tool and/or the dressing tool are rotatably driven, whereby the dressing surface of the dressing tool has a different curvature than the spherically curved surface portion of the workpiece.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to German Patent Application DE 10 2016 125 206.9, filed Dec. 21, 2016.

BACKGROUND OF THE INVENTION

The present invention relates to a method and a machine for processing a spherically curved surface portion of a workpiece, as well as a dressing tool for the finishing tool.

With known finishing process for spherically curved surface portions of a workpiece, in contrast to sanding, the workpiece as well as the finishing tool are rotatably driven, whereby their axes of rotation are arranged relative to one another at an angle. The finishing tool containing grains bound to its finishing surface self-trims or dresses during finishing of relatively hard workpieces on the machining surface section and thus has the same curvature as the surface section of the workpiece to e machined. If, in contrast, the workpiece is relative soft or if the finishing tool has a high bond hardness of the grains, then such a self-trimming or self-dressing is no longer provided.

It is therefore known to dress the machining surface of the finishing tool by means of a diamond of the complementary shape to dress the surface section of the workpiece, whereby the cutting edge of the diamond must be guided in a contour-controlled manner along the machining surface of the finishing tool. This requires a relatively high equipment expenditure for the contour control of the diamond, since the track for the different finishing tools must be adjustable.

It is also known to use a dressing tool, whose dressing surface has the same curvature as the workpiece to be machine with the finishing tool. In this connection, for example, bye diameter of the spherical workpiece is slightly reduced and subsequently coated with diamonds. The workpiece coated with diamonds thereby forms a dressing tool, whose outer diameter corresponds with the outer diameter of the respective workpiece to be machined. In this regard, it is disadvantageous that for each diameter, a separate dressing tool must be made and that this must be exchange when the workpiece to be machined is change in the machine.

SUMMARY OF THE INVENTION

An object of the present invention, therefore, is to overcome the disadvantages associated with the state of the art and in particular, to provide a machine and a dressing tool, with which the expense for dressing different finishing tools is reduced.

The object is solved in particular by a method for finishing a spherically curved surface portion of a workpiece with a finishing tool having a machining surface, including at least the following steps:

finishing the surface portion of the workpiece, whereby the finishing tool, with at least one part of the machining surface, is brought into contact with at least one part of the surface portion of the workpiece and the workpiece and the finishing tool are rotatably driven,

dressing the finishing tool with a dressing tool having a curved dressing surface, whereby the dressing tool, with at least one part of the dressing surface, is brought into contact with at least one part of the finishing surface of the finishing tool and the finishing tool and/or the dressing tool are rotatably driven, whereby the dressing surface of the dressing tool has a different curvature than the spherically curved surface portion of the workpiece.

The invention relates, therefore, exclusively to the finishing of a spherically curved surface portion, which also can be designated as a cup-shaped or spherical surface.

The finishing tool, in articular, has bonded grains and preferably is formed as a cup wheel. For the finishing process, the finishing tool with the machining surface is placed onto the surface portion of the workpiece to be machined, whereby, during the finishing process, the finishing tool as well as the workpiece are rotatably driven, whereby, in particular, the axes of rotation are positioned to be at an angle to one another.

The dressing of the finishing tool can take place before the first use of the finishing tool, but also as intermediate dressing between the fishing of two workpieces or even in an interruption of the finishing process of a workpiece.

For dressing, the dressing surface of the dressing tool is placed on the machining surface of the finishing tool, whereby, preferably, an axis of rotation of the finishing tool and an axis of rotation of the dressing tool are arranged parallel to one another and preferably also displaced relative to one another. It also can be provided that for dressing, the dressing tool as well as the finishing tool are rotatably driven about their respective axes of symmetry. Alternatively, it also can be provided that only the finishing tool is rotatably driven, so that the machining surface of the finishing tool is moved along the dressing surface of the stationary dressing tool. It also could be provided that the rotatably driven dressing tool is moved in a plane orthogonally to the axis of symmetry of the finishing tool along the finishing tool. In any case, it is not necessary that a path-controlled motion is performed, which determines the shape of the dressed machining surface of the finishing tool. During the dressing, however, a radial, relative movement between the finishing tool and the dressing tool can take place, in order to maintain a constant abrasion rate.

The invention contemplates in its basic concept that the dressing surface, with reference to the amount of its curvature or the course of its curvature along the rotational axis of symmetry is formed differently than the surface of the workpiece to be finished, which is spherical with a radius of curvature. This offers the advantage that a dressing tool for dressing different finishing tools can be used, which are used for finishing surface portions of workpieces with different radii of curvature.

In particular, the dressing surface of the dressing tool is rotationally symmetric about an axis of rotation and has an aspherical shape, whereby the dressing surface, in particular, has a hyperbolic or parabolic curvature that runs along the axis of rotation. The dressing surface, then, cannot be characterized has having a precise curvature radius; in addition, the curvature radius changes along the axis of rotation. In particular, the course of the curvature along the axis of rotation can be described as a function of the height along the axis of rotation as hyperbolic or parabolic.

Alternatively, it can be provided that the dressing surface has a spherical curvature, at least in one section, whose curvature radius different from the curvature radius of the spherical surface portion of the workpiece. While with an identical value of the curvature radius of the dressing surface and the spherical surface portion of the workpiece, the dressing surface is in continuous contact in the circumferential direction with the surface portion of the workpiece, with this embodiment, the dressing surface is only in contact with the machining surface of the finishing tool only at this position in the circumferential direction.

In particular, the diameter of the dressing surface can be smaller than the diameter of the machining surface of the finishing tool.

According to the present invention, the machining surface of the finishing tool, after dressing, in particular, along the rotational axis of symmetry, has a different curvature than the surface portion of the workpiece. This has the result that the dressed machining surface of the finishing tool, at least at the beginning of the following finishing process, does not completely contact the surface portion of the workpiece. In particular, after dressing, only a small region of the dressed machining surface of the finishing tool contacts the surface portion of the workpiece. This is advantageous with regard to relatively hard workpieces, in that a higher specific surface pressure (this corresponds with the pressure on the surface portion per grain of the finishing tool) can be achieved. During the finishing process, if necessary, an auto-dressing of the finishing tool on the workpiece can take place, whereby for increasing the specific surface pressure, an intermediate dressing of the finishing tool can be provided.

In order to increase the ability of the finishing tool, in particular, in an edge region, it can be provided that an axial face of the finishing tool is dressed simultaneously with the machining surface of the finishing tool. By the dressing of the axial face, a circular, axially oriented face is made on the finishing tool. This means, in particular, when the finishing tool is in the form of a cup or face wheel, that the edge facing the workpiece is not tapered, rather contains a blunt projection, so that this end region is less susceptible to breakage.

The shape of the dressed machining surface of the finishing tool, then, is determined by the axial or radial relative positions between the dressing tool and the finishing tool. Thus, with contact of the machining surface of the finishing tool on a region of the dressing surface with a greater curvature, the machining surface maintains the corresponding curvature.

It can be provided, in particular, that a dressing tool for dressing the machining surface of finishing tool can be brought into contact successively with the machining surface of the finishing tool in different positions.

In particular, the dressing tool is used for different finishing tools, which are provided for finishing spherical surface portions of workpieces with different radii of curvature.

This object is solved by a machine for finishing a spherically curved surface potion of a workpiece, which, in particular, is equipped for performing the inventive method, with the workpiece, with at least one rotatably driven workpiece holder, in which the workpiece is positionable, and with at least one rotatably drivable finishing tool holder, in which a finishing tool having a machining surface is held, as well as a dressing tool having a curved dressing surface, whereby the dressing tool can be brought with the dressing surface into contact with the machining surface of the finishing tool, whereby the dressing surface of the dressing tool has a different curvature than the spherical surface portion of the workpiece.

The machine, in particular, can have multiple machining stations, wherein in one of the machining stations, the finishing tool older is arranged to be rotatably drivable. The finishing tool holder, in particular, can be adjusted in a translatory manner and also can be pivoted relative to a workpiece holder. The dressing tool can be arranged likewise in a dressing tool holder, which is adjusted to the finishing tool holder in a translatory manner and if necessary, also can be pivoted. Also the dressing tool holder can be rotatably drivable. In particular, multiple workpiece holders can be mounted on a circular table, so that multiple workpieces can be processed successively at the machining stations with the finishing tool holder.

In one embodiment of the invention, it can be provided that the dressing tool is arranged in a workpiece holder and this workpiece holder thereby forms the dressing tool holder.

This object is also solved by a dressing tool for dressing a finishing tool, with a dressing surface having a curvature with a cutting ability that is rotationally symmetrical and which runs along the axis of rotation, which for dressing is brought into contact with a machining surface of the finishing tool, whereby the curved dressing surface, in particular, has an aspherical form along the axis of rotation. The curved surface, on the one hand, is thus rotationally symmetrical to an axis of rotation, and generally has different radii of curvature along the axis of rotation, radii of curvature, in particular, which are continuously merging.

The curved surface of the dressing device is therefore neither completely formed as a spherical segment nor conically or with only a minimum radius of curvature.

In order to dress an axial face of the finishing tool simultaneously with the machining surface of the finishing tool, a planar, circular and axially oriented dressing surface can connect to the curved dressing surface of the dressing tool. The dressing tool, thus, can be oriented to the finishing tool during the dressing process, such that either the machining surface and the axial face simultaneously are finished or that first the machining surface is dressed with the curved dressing surface and next, the axial face of the finishing tool is dressed with the circularly arranged dressing surface.

The cutting ability of the dressing surface, in particular, is achieved by a coating with diamonds. Alternatively, the cutting ability also can be achieved by forming the dressing surface to be abrasive, such that the finishing surface of the finishing tool containing the bound grains can be removed from the abrasive dressing surface of the dressing tool.

In particular, the curved dressing surface has a continuously changing curvature along the axis of rotation, whereby this, in particular, has a hyperbolic or parabolic course along the axis of rotation.

Alternatively, it can be provided that the curved dressing surface has multiple, spherically formed sections, whereby the sections have different radii of curvature. Thus, on one dressing tool, multiple dome-shaped sections are formed, which, respectively can be used for the corresponding application for dressing the finishing tool.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a finishing tool and a dressing tool in a first relative position to one another;

FIG. 2 shows a detail of FIG. 1;

FIG. 3 shows the finishing tool and the dressing tool in a second relative position to one another;

FIG. 4 shows a detail of FIG. 3;

FIG. 5 shows the finishing tool and the dressing tool in a third relative position to one another; and

FIG. 6 shows a detail of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The figures show a cup-shaped finishing tool 11, which has a machining surface 2 on its lower, inwardly directed edge. The finishing tool 1 additionally has an axial face 6.

In the figures, a dressing tool 3 with a curved dressing surface 4 and an axially aligned, planar dressing surface 7 is also shown. The dressing tool 3 is formed to be rotationally symmetrical about an axis of rotation 5. The dressing surfaces 4 and 7 are diamond-coated.

It should be recognized that the curved dressing surface 4 is in fact rotationally symmetric relative to the axis of rotation and the curvature along the axis of rotation 5 originating from the planar dressing surface 7 is continuously reduced. The curved dressing surface 4, therefore, is not spherically shaped.

For dressing, the finishing tool 1 and the dressing tool 3 are first brought into the position shown in FIG. 1, in which the planar dressing surface 7 of the dressing tool 3 is brought into contact with the axial face 6 of the finishing tool 1, and in which the curved dressing surface 4 of the finishing tool 1 is brought into contact at least partially with the machining surface 2 of the finishing tool 1. In this position, for dressing, the finishing tool holder 1 and, if necessary, also the dressing tool 3 are rotatably driven.

After dressing, the machining surface 2 has essentially the curved development or course as the curved dressing surface 4 (see FIG. 2). Also, the axial face 6 of the finishing tool 1 would be dressed, such that in this region, a thickness of the pot wall is provided that prevents breakage. In principle, the finishing tool 1 dressed in this manner could subsequently be used for a finishing of a workpiece with a spherical surface portion.

It also is possible, however, that the machining surface 2 of the finishing tool 1 is dressed in a further step. In this connection, the finishing tool 1 is brought radially outward and axially downward into the position shown in FIG. 3. After dressing in this position, the machining surface 2 has the form shown, in particular, in FIG. 4.

In a further step, the dressing tool 3 can be brought into the position shown in FIG. 5, whereby in this regard, the dressing tool 2 again would be displaced radially outward and axially downward. After the finishing step, the machining surface 2 has three sections, which connect to one another in the axial direction, as shown for example in FIG. 6.

The specification incorporates by reference the disclosure of German Patent Application DE 10 2016 125 206.9, filed Dec. 21, 2016.

The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.

REFERENCE NUMERAL LIST

-   1. Finishing tool -   2. Machining surface -   3. Dressing tool -   4. Dressing surface -   5. Axis of rotation -   6. axial face -   7. planar dressing surface 

We claim:
 1. A method for finishing a spherically curved surface portion of a workpiece with a finishing tool (1) having a finishing surface (2), including at least the following steps: finishing the surface portion of the workpiece, wherein the finishing tool (1), with at least with one part of the finishing surface (2), is brought into contact with at least one part of the surface portion of the workpiece, wherein the workpiece and the finishing tool (1) are rotatably driven; dressing the finishing tool (1) with a dressing tool (3) having a curved dressing surface (4), wherein the dressing tool (3), with at least one part of the dressing surface (4), is brought into contact with at least one part of the finishing surface (2) of the finishing tool (1), and wherein the finishing tool (1) and/or the dressing tool (3) are rotatably driven, wherein the dressing surface (4) of the dressing tool (3) has a different curvature than the spherically curved surface portion of the workpiece.
 2. The method according to claim 1, wherein the finishing tool (1) and/or the dressing tool (3) is substantially rotatably driven during dressing.
 3. The method according to claim 1, wherein the dressing surface (4) of the dressing tool (3) is formed rotationally symmetrical to an axis of rotation (5) and has an aspherical curvature, wherein the dressing surface (4), has a hyperbolic or parabolic curvature running along the axis of rotation (5).
 4. The method according to claim 1, wherein the dressing surface (4) has a spherical curvature, wherein a radius of curvature of the spherical curvature differs from the radius of curvature of the spherical surface portion of the workpiece.
 5. The method according to claim 1, wherein an axial face (6) of the finishing tool (1) is dressed simultaneously with the finishing surface (2) of the finishing tool (1).
 6. The method according to claim 1, wherein a dressing tool (3) is used for dressing different finishing tools (1), wherein the different finishing tools are configured to finish spherical surface portions of workpieces with different radii of curvature.
 7. A machine for finishing a spherically curved surface portion of a workpiece, comprising: at least one rotatably driven workpiece holder in which the workpiece is arranged; at least one rotatably driven finishing workpiece holder, wherein a finishing tool (1) having a finishing surface is held in the finishing workpiece holder; and a dressing tool (3) having a curved dressing surface (4), wherein the dressing tool (3) with the curved dressing surface (4) is configured to be brought into contact with the finishing surface (2) of the finishing workpiece (1), wherein the dressing surface (4) of the dressing tool (3) has a different curvature than the spherical surface portion of the workpiece.
 8. The machine according to claim 7, wherein the finishing tool holder and a dressing tool holder that holds the dressing tool (3) are radially and axially adjustable relative to one another.
 9. The machine according to claim 7, wherein the dressing tool (3) is arranged in a workpiece holder and the workpiece holder thereby forms the dressing tool holder.
 10. The machine according to claim 7, wherein an setting angle between the finishing tool holder and the dressing tool holder is adjustable.
 11. A dressing tool (3) for dressing a finishing tool (1), comprising: a curved dressing surface (4) having a cutting ability and a rotationally symmetrical curvature along an axis of rotation (5), wherein the dressing surface (4) is brought into contact with a finishing surface (2) of the finishing tool (1), wherein the curved dressing surface (4) has an aspherical shape.
 12. The dressing tool (3) according to claim 11, wherein a planar, circular, and axially aligned dressing surface (7) contacts the curved dressing surface (4) for dressing a face (6) of the finishing tool (1).
 13. The dressing tool (3) according to claim 11, wherein the curved dressing surface (4) has a continuously changing curvature along the axis of rotation (5).
 14. The dressing tool (3) according to claim 11, wherein the curved dressing surface (4) has a hyperbolic or parabolic progression.
 15. The dressing tool (3) according to claim 11, wherein the curved dressing surface (4) has multiple, spherically shaped sections, wherein the sections have different radii of curvature. 